Process for the production of nitric acid



Jan. 2, 1940.

lH. A. BEEKHUIS, JR`

PROCESS FOR THE PRODUCTION OF NITRIC ACID 2 Sheets-Sheet 1 BY J7.

ATTORNEY Jan. 2. 1940. H. A. BEEKHuls, JR 2,185,580

PROCESS FOR THE PRODUCTION OF NITRIC ACID INVENTOR ATTORNEY lis lancewith the process of this invention, I have discovered it is feasible tooperate under condil tions which correspond to a nitric oxideconcentration equivalent to-a partial Vpressure of NO below 0.01atmosphere, for example 0.0003 atmosphere or even less, and a highlyconcentrated nitric acid may readily be produced bythe direct absorptionof nitrogen.peroxideinthe presence of chlorine. The nitric acid. thusobtained contains chlorine (free and combined) which may, however, bereadily stripped from the concen'- trated nitric acid by heatingtheacid, prelferably While passing a gas such as'oxyg'e`n"in"contac t Withthe heated acid. Chlorine, chiey in the iorrn of nitrosyl chloride, and`sornenitrogen perl-- oxide gas my thus be evolved-from the' nitricacidi and a pure concentrated nitric-#acid product ob-- In carrying outvthe process of this invention for the production of nitric acid,nitrogenjper oxide is reacted rwithan aqueous nitric acidv con-- tainingsubstantially,70v parts or AmoreQI-INOs .to 30'pa'rts H2O (correspondingto substantially 70% v orv stronger nitric acid'solution) in thepresence of 'fr ee'chlorine to form a more concentrated nitric'acidcontaining .atleast 70 parts HNO's to 30 lparts H2O., The reaction iscarried out in a reaction mixture-containing al concentration ofnitrogen peroxide and a nitric: acid for which the equilibrium partialpressure of nitric oxide is below 0.01 atmosphere. Ilie concentration ofchlorine in a nitric acid containing '70 parts ormore I-INOa to 30 partsH2O. formed by .reaction of nitrogen peroxide and chlorine is ameasure'of 1the vinfluence of` the chlorine upon '.thereaction inmaintaining a low partialpres'sure oinitric oxide inthe` reactionmixture.' Accordingly, in carry-.- in g out the processv of thisinvention the reaction mixture contains sulicient free chlorine toreduce the partial 'pressure ofythe nitric oxide to below theVequililqriinn partialpressure of NO in the absence or" chlorine andtoformanitric'acid containing morethan 0.5%, land preferably about 1%ormor'e total chlorine (calculated fas HC1) which is present in theacid'y as'ifreev4 chlorine, ni-

trosyi chloride' and hydrogen-chloride. i1 y The chlorineinayy bepresent 'n the" liquid phase 'of thev reaction `mixture,.in.theproporti'ons' of, for example, 1 rnol chlorine to 5 vto 100 mols oftotalnitrogen peroxide (present both" as NO2 and N204) preferablyl 1 molchlorine to. 15 to 30 inols total nitrogen peroxide.y ySincetl'iedistribution ot Athe chlorine and `nitrogen peroxide between the gas andliquid phases-ofthe reaction mixture differs, the aboveproportions of 1mol chlorine to 5 to 10,0 Inols and A.to 115 to 30` mols nitrogenperoxide inthe liquid phase lcorrespond y to 1 mol chlorine to 1 to20fmols rand to 3 to 6 m ols,respectively, rif-.nitrogen peroxide in'the gas phase of the reactionlmixture. The` partial pressure of nitrogenperoxide-in thereaction mixtures should be more thanf0.1v atmosphere.Nitragen peroxide andi-chlorine iny contact with the nitricacidWillfcontain nitrosyl'chloride and this orother gases, for example,oxygen and nitrogen, may be present in a nitrogen peroxidechlorine gasinitially passed into l.contact'f'vvith ing 'under pressureanaqueousnitric acid or Wa` ter and lqui'siinitlogenreroxide and Chlorine:in

invention,v l l The reaction oi the aqueous nitric acid, nitro-z underconditions that i' proportions such that either initially ,or after jre-I action of a portion ofthe Water with the 'nitrogen peroxide thereaction mixture contains aquef ous nitric acid containing about.ll'parts or more HNOa vto 30 parts H20, nitrogen peroxide and vsiredfurther reaction of the Water in the aqueousxacidwith the nitrogenperoxide :in accord- Y* ance With-theprocess of this invention. ,"Ihere` action mixture. maybe prepared byv vintimately contacting aqueousnitric acid'containingA sub- 2,

stantially %.or more vI-INOs'with v gaseous nitrogen peroxide andchlorine. f lIn this case also- 1 the aqueous nitric acid. initially maycontain?"15 l much less. than-70% HNOS `and by reaction with partof thevnitrogen peroxide and chlorine atl tain a'concentra'tion ofsubstantially 70% and-the j reaction of this acid and the nitrogenperoxidev and chlorine then: continue to form ja 70%" or stronger nitricacid under the4 conditions herein described for carrying outthe-processofrvthisf gen peroxide and'lchlorine may be carried out' at a widerangepf.y temperatures, torexample,`

rom0 C. to vabout-"110 C.be1ow the boiling point of water at thepressure`under which the reaction mixture is maintained. Itis preferred,however, tomaint'ain the reacting materials at a temperature ofabout. to'70 C. yThe'con centratedl nitric vacidproducty obtained maybe heatedunderatmospheric pressure to a tempera--`v ture above 50C. to free it ofchlorine and. Chlo-1, rides and their evolutionvfromlthe acidrnay be*facilitatediby both heating the= acid and'passin'glf in'contactwitli'itan. inert gas suchlas oxygen.

p'eroxide, chlorine and 'rnitrosyl chloridey inthe gas', ratio V`-ofWaterto nitricfacid' inthe liquid and'temperature. The process ofthisinvention f.

may be carried out toforma nitric acid containin g7`0% or more HNQ by'contacting a gas con-"1v f taining nitrogenperoxide and chlorine withsub-v 'stantially 170% or vstronger aqueous nitricv acid isatleastequalto theantilog` (1o) o fA (0.02T-6.6)

Where: (NOgLKCl) and (NOCI) are the partial pressures in atmospheres n.ofY in itrogen vperoxide as NO2, `chlorine andnitrosyl' chloridein thegas .mi .With v which [the 701%.' or fstronger nitric 'acid' formied'byreaction of the'nitrgen peroxide with;

a weaker acid'is lastfcontacted; T is the temperature indegreesjalczsolute of the reacting gas and vl nitric acid where-the"aciugisiastontactedmth the4 leas.; "endg j! squarev of the nitric 'acidVapor; pressure A(in atis the ratioofjv the water Vapor pressure to. the

containingy substantially 70. barils or: more HNO:

containing nitrogen` peroxide and chlorine td Ilesact therewith to form70 orstrongernitric acid in accordance .with this invention.

OfA the total nitrogenpe'roxide :present in thev reaction mixture onlythat'present as NO2 is ineluded in the above formula. From the .partialpressure of total nitrogen vperoxide-inthe gas,

where l(N204) andiNz) represent the partial pressures of the respectivegases and T is the temperature in degrees absolute ofthe gas' containingthese two constituents.

This invention is of particular' value in the vproduction of highlycon'centratednitric acidcontaining, for example, 95% up to 100% HNOafrom .gases containing nitrogen peroxide.

As pointed out above, relatively dilutek aqueous nitric acid solutionsmay be obtained by absorption'of nitrogen peroxide in water or'aqueousnitric acid solutions, but to. make acids'of a high strength' requiresspecial provisions tor increase the rate 'of oxidation of the nitricoxide; nor may aqueous acids containing less than 70% HNOS which may ibe prepared by absorption of nitrogen peroxide be distilled to producehighly concentrated acids. Nitric acid and water form a constant boilingmixture containing about 68% HNO3 so that no acid of a higherconcentration than 68% may l be obtained by distilling va weaker acid.'Ihis invention, therefore, comprises a process wherein` a nitrick acidcontaining at least 70% HNOa is formed byA reaction of nitrogenyperoxide with water n'an aqueous nitric acid, and this relativelyconcentrated acid is thenv fractionally distilled to yield a dilutenitric acid distillate and a highly concentrated nitric acidproduct,which may con-l tainjupwardly of 95% to 100%,.HNO3. An embodiment ofthis a'sp'ectvof` the inventioncomprises reacting nitrogen peroxide withan' aqueous nitric acid containing,` say, 6 8 to 74% I-INOs in thepresence of )chlorine until the acid cone tains about 80% to 90%` ,HNOaThis more concentrated acid is fractionally distilled to obtaina'relatively dilute nitric acidas a residue and a or up to 100% HNOs asa distillate.

For a furtherunderstanding of this invention reference is had to thefollowing detailed description of processes for the production of aconcentrated nitric acid which are illustrated-in the ac'- fconcentratednitric acid containing about 95%.

companying drawings. In the drawings- Fig. 1 shows a process for thereaction of nitrogen peroxide, chlorine and water to form a concentratednitric acid and nitrosyl chloride, and

Fig. 2 illustrates a modification of the process of Fig. 1.

Referring to Fig. 1 of the drawings, the numeral l indicates anabsorption tower into the upf per portion yof whichian aqueous nitricacid containing, for example, about 68% to '74% `HNOs is introduced; Amixture of nitrogen peroxide and chlorinevis introduced intothe bottomof tower l and is passed upwardly through the tower y' bined as nitrosylchloride.

'also 'contain chlorine -in combinationas hydroin contact with thenitric acid descending therethrough at a temperature of, for example,about 30 C. There iiows off from the bottom ofv the tower ya relativelyconcentrated aqueous nitric acid solution containing ysome dissolvednitrogen peroxide andchlorine, particularly chlorine comchloric acid.This acid solution is introduced -or other gas inert towards vativelysmall proportions "desorber 2.

The nitric acid may `intofthe top of tower 2 which operates asa'desorber. Tower 2 is provided' with a heater to lheat the nitric aciddescending throughl the'tower" toa temperature'within the range of 50 to100 C. Oxygen is also 'introduced into thebottom of the tower and passedupwardly in contact With the descending heated nitric acid. The gasesevolved from the acid yin the desorber, together withl oxygen introducedthereinto pass from the top of the desorber intolthe bottom ofabsorption Instead of heating the nitric acid in desorber' l2 andtreating it at an elevated temperature with a relativelyv small amountofy oxygen gas as described above, the acid from may be treated indesorber 2 by means of air ynitric acid passed through the desorber inamount suliicient to remove from theacid at ordinary atmospherictemperatures nitrogen peroxide, nitrosyl chloride and chlorinelcontained therein. acid the gas leaving they desorber will contain relvof nitrogen peroxide, nitrosyl chloride and chlorine which mayberecovered, if desired, by absorption in water or the gas leaving thedesorber may be discharged without further treatment. i

The relatively dilute nitric acid introduced into absorption tower lis'treated with the gases 'containing nitrogen peroxide and chlorine insuch amount that the nitric acid solution after treatment in desorber 2contains from 80% tol 90% HNOg. This relatively concentratednitric acidis introduced into ythe mid-portion of a tower 3,

the bottom of which is provided with a heater. In this tower theentering nitric acid is passed downfrom the entering nitric acid and themixture of nitric acid and water vapors pass upwardly through the towerin contact with reuxed nitric acid,` and thence to a condenser 4 wherethey are condensed-to form nitric acid. 'A portion of this condensate isreturned to the top of tower 3 as a nitric acid reflux. The amount ofreiiux is so regulated that upon condensing thefnitric acid vaporsleaving the top oi the tower, a nitric acid of about 95% to 100% HNOs isformed.A This relatively concentrated nitric acid, as noted above, isinf part returned as reflux to the top of tower 3 and therernainder iswithdrawn as a concentratednitric acid treatment of the moreconcentrated acid introduced intol the mid-portionof this tower fromSufficient vapors are evolved from this nitric acid inthe bottom oftower 3- so lthat it contains from'68%to '74%l HNOs which is withdrawnfrom the bottom of the tower and is returned to the upper portion ofabsorption; tower I for treatment with the gas containing 'nitrogenperoxide and chlorine.

The gases from the top of absorption tower l `contain nitrogen peroxideand nitrosyl chloride together with some chlorine and oxygen. These ifgases are passed through a heat exchanger 5 and thence to an oxidationchamber (i, where nitrosyl.

ychloride is oxidized to nitrogen peroxide and chlorine by means ofthevoxygen contained inl l'the-gas.'l The hot gaseous products of thisoxidaabsorption tower l In thus treating the product of this process.Therelatively dilute nitric acid which passes downwardly into the bottomof tower 3 is heated to 'provide the nitric acid 'and water vapors foriso tion treatment pass through heat exchanger 5 serving to preheat theincoming gas containing nitrosyl chloride and are then introduced intothe nitrogen peroxide gas on its way to absorption tower I. A portion ofthe gases from the top of absorption tower I are continuously withdrawnto a scrubber 'I where they are washed with water to absorb the nitrogenperoxide, nitrosyl chloride and chlorine, as well as any nitric acidwhich may be present in this withdrawn gas. The unabsorbed inert gasesare vented from the top of scrubber 1 while the dilute aqueous solutionfrom the bottom of scrubber 'I is introduced into the top of absorptiontower I. v

In carrying out the process described above and illustrated in thedrawing, the proportions of water introduced into scrubber 1 and thenceinto absorption tower I and of nitrogen tetroxide gas introduced intothe bottom of absorption tower I are such as to form the desiredrelatively concentrated nitric acid of to 90% HNOS leaving tower I andthe to 100% acid from tower 3. Since theoretically all of the chlorinegas present in the nitrogen peroxide gas introduced into the bottom ofabsorption tower I may be recovered as nitrosyl chloride, which may beoxidized to nitrozen peroxide and chlorine and reintroduced intoabsorption tower I, once the desired proportion of chlorine has beenintroduced into the cyclic system in which the procedure described aboveis carried out, no`

further addition of chlorine is required except that necessary to makeup for the chlorine losses from the system, for example, that lost withthe inert gas withdrawn from scrubber 1 or the unavoidable losses oimaterials always encountered in the actual carrying out of chemicalprocesses. The oxygen required for substantially complete reaction ofthe nitrogen peroxide with the water is introduced into the bottom ofdesorber 2 and thence passes to obsorption tower I. In the continuousoperation of the process described above the nitrogen peroxide andoxygen are introduced into the system in the proportions of about 4 molsof nitrogen peroxide for each 1 mol of oxygen, together with the vrequired amount of make-up chlorine. As illustrative of the approximatecomposition of the gases in the process described above,it may be saidthat thev gas leaving absorption tower I passing to heat exchanger 5 maycontain about 0.5 mol of nitrogen peroxide to 1.5 mols nitrosyl chlorideto 0.5 mol chloride to l mol oxygen. The gas after oxidation of nitrosylchloride in oxidation chamber 6 may contain 1.5 mols nitrogen peroxideto 0.5 mol nitrosyl chloride to l mol chlorine to 0.5 mol oxygen. Tothis gas there is added about 2 mols of nitrogen peroxide for every 1.5mols of nitrogen peroxide in the gas from the oxidation chamber 6, andabout 0.5 mol oxygen is introduced into the bottom of desorber 2 forevery 2 mols of nitrogen peroxide introduced into the gas leavingoxidation chamber 5. These ratios are for the nitrogen peroxidecalculated as NO2. If desired, the distillation and rectification ofnitric acid in tower 3 may be carried out under a reduced pressure belowatmospheric. The acid from desorber 2 may also, if desired, be treatedwith concentrated sulfuric acid toobtain a more concentrated nitric acid(95% to HNOa) instead of being subjected tothe distillation treatmentdescribed above.

In carrying out the process illustrated in Fig.

1 and described above, the concentrated nitric acid flowing from thebottom of absorption tower l win contain about 1% chlorinettoth .freeandcombined), calculated as HC1. Substantially all of this`chlorinecontent` of the solution -will be.. evolved vas nitrosylchloride and 'chloride in heating the acid in vtower 2. Referring toFig. 2,'whichi1lustrates asecond procedure operatingin accordancewiththis invention, absorption tower 8 and stripping tower Scorrespondto towers I and 2 of the apparatus of Fig. 1. A gas of the followingcomposition ini per cent by volume is passed vat onev atmosphere throughpipe I0 into the bottom of tower 8.

acid and gases in tower 8 are maintained at about 40 .C. A nitric `acidof more than 80% HNOa strength (more than 80 parts I1NO3 Ato every 20`vparts H2O) containing dissolved NO2" and chloride equivalent to about1% HC1 is withdrawn from the bottomv of tower 8 and is -passed l PercentTotal nitrogen peroxide 62.5 Chlorine 13.5

Nitrosyl clrloride 6.5 Oxygen 17.4

into the topY of tower 9 in which it is heated and treated with oxygento evolve the chlorine con` tent of the acid. A concentrated nitric acidcontaining above 80% HNO3 flows from the bottom of tower 9 through pipeII.

In carrying out theprocess of this example, the partial pressures in the.gas introduced into the bottom of tower 8 (i. e., the gas with whichthe acid` containingl above 80% HNOa, formed by reaction of the nitrogenperoxide with weaker acid, is last contacted) A:will be:

:.he temperature of the reactinggas and liquid at the bottom of thetower is 313 absolute.

Since an acid containingl 56.5% HNOa is intro-4v Atmosphere raaf4Nitrogen peroxide 0.31 Nitrogen tetr0xide 0.23 Chlorine 0.166 lNitrosyl chloride 0.08 Oxygen 0.214l

the liquid ows downwardly inthe tower, av u liquid containingsubstantially 70 parts `.'Ii-INKOa to 30 parts H2O (70% HNO3) initiallycontacts was gas containing nitrogen `peroxide and chloe :rine at apoint in the tower intermediate between the top and bottom. Substitutingappropriate values in the formulae Since 1.35 .is greater than 0.456,the condition 4with respect to gas 'composition' and reaction Thevunreacted nitrogentperoxide and chlorine@ l'Gli accompanied by nitrosylchloride formed by reaction of the' chlorine leaves the top of tower 8"through pipe I2. Gases fro-m the top of tower 9 pass' through a pipe I3vand may be mixed with return to tower 8.

top of towers 8 and 9 may be separately With-` thegases. leaving the topof .tower 8 and the .mix-

turetreated as .desired, lfor* example', asin the process illustrated inFig. 1, to oxidize the `nitrosyl chloride to' nitrogen peroxide andchlorine for If desired, the gases from the drawnthrough pipes I4 and l5separately treaty ed in any desired manner. f

` the reaction mixture.

As pointed out above, the reaction of liqueed nitrogen yperoxide 4withan aqueous vnitric vacid may be promoted by .the presenceA of chlorinein In carrying out a processinH accordance with this modification of theinvention, "a mixture of liquefied nitrogen peroxide an'd"chlorinerand-Van aqueous nitric .acid containing substantially 70% or more HNOaare'reactedin an autoclave while maintainingthe reactingmaterials at a.temperature and pressure at which the nitrogen .peroxide and 'chlorineremain as a liquid. In such a process a large excess'of nitrogenperoxide may be employed such that two liquid phases are formed, one ofwhich.

is a solution-in nitric acid of nitrogen peroxide and chlorine and the`other a solution in nitrogen peroxide of chlorine and nitric acid. Withthese two liquid phases present in thereaction mixture,

, the reacting materials' are supplied in amountsA "by the formula suchthat the partial pressures of NO2, C12, NOCl, H2O .and HNO3 bear therelationship set forth is at least equal to the analoges cf moer-.6.6)

.and the concentrated nitric acid yphase which is latedfat lHC1.

Since numerous changes and modifications may be made in the particularprocesses described abovewithout departing from ,the scope of theinvention,` the examples given are to be formed contains 0.5% or morechlorine calcuunderstood as .being illustrative of the 'invention whichcomprises a gas phase containing nitrogenr vso rather than limiting it.

This applicationvis a continuationrinepart of my copending applicationSerial No. 697,240, filed November 9, 1.933. v,

Iclaim; .1. The process for the production of '70% or stronger nitricacid which comprises contacting vnitrogen peroxide and .chlorine withanaqueous nitric-acid.containing substantially 70 parts or more HNO3 .to30 parts H2O in a reaction mixture peroxide and chlorine in amounts suchthat is last contactedlT is the temperature in degrees absolute of thereaction mixture'in which the nitric acid is last contacted with thelgasphase, and

is the ratiov of .the water vapor pressure to the square. ofthe.nitricacid vapor pressure at tem. perature-T over a nitric acid-water`solutioncon-v tainingi'the" samevproportions of HNOS and H2O 2,185,580 fy t f many y 'zo' parts orvv more I HNoas-to, soppam` H20.

nitric acid is last contacteclwith the gas'and which initiall7jcont'ctsfwithsaid nitrogen peroxide and chlorine and-"anitricvacid'containing at least '70 parts-HNOE to v30'partsvI-I2O which ismore` concentrated 'than' said aqueous nitric acid is' formed" byv'reaction' 'of said nitrogen peroxide and-chlorine with`ywatercontained inthe aque-` ous nitric acid. y. v y 2..'.The processfor the-production of 70% or stronger nitric acidwhi'ch comprisescontacting gas` containing nitrogen'lperoxide and chlorine withanaqueous nitric acid containing substantially 70 .parts'or' more HNOsto 30 parts H2O, peroxide and chlosaidl gas containing nitrogen rineyinvamounts such that N02 3 C12 i H2o isat .least 'legen-t0 meantime@ ofozrgsrf where:` NO2),1(C1`2) 'and V(NOCI) are the partial pressures(inatmospheres `fof N027, C12 and NOCI,

lli

respectively, in the gasv with which the 70% or" strongernitricacid'forrned byr'eaction'of the ni'- trogen yperoxide with :saidaqueousnitric acid is last contacted,` 'T1 is the temperature; in=degrees absolute of 'the gas and" nitricfacid where 'the' nitric acidis last 'contacted''with'the gas, and

(HNOS)2 is the ratio of 'the water' vapor pressure to the sqnar'e of thenitric acidvaporpressure attem-l perature' T overa nitridacidwatersolution containing'jthe same proportionsjof HNOs andQI-,IzO

tianyio parte @more Hnosy t saparts' H20 which initially contacts? with"gas containing nitrogen lmroxidel and'chlorinenand a nitric acidcontaining at leastA 70`partsjI-INO3 to 30 parts I-IaOwliich4 is moreconcentrated vthan' said aqueous nitric acid is'forined byn're'actionof'said 'nil trogen peroxide and chlorine withrwater,l contained in theaqueousinitricacid.

They process'for the vproc'luction oi`"70% or stronger nitric acidWhich"`co'mprises contacting a gas lcontaining5.(l% or morejnitrogenperoxide and chlorine in theproportionsof l mol -of free* chlorine forevery-l to 20 mols of "nitrogen perv oxide with an aqueous nitric acidsolutioncon- I taining substantially '70 parts or more HNOa to 30 partsH2O;saidgas'cont'aining nitrogen peroxide,

.chlorine andvnitrosyl chloride in amounts vsuch that 'l ,f i y(Newman-(Hic) v (NoC1),(/i7rNo3)2;@

is at least equal to the antilogcio)` of (oom-@ssii where: (NO2), (C12)`and (NOCI) are the partial pressuresfn atmospheres) of-'NOaClz and NOCl,i

respectively,` in the.gas'with which the 70% or stronger .nitriclacid"oririeddoyreaction of the `nitrogen peroxide with saidy aqueousnitric Iacid is last contacted, Tis' thetemperature indegrees absoluteof thezgas and'nitriciacid where the is .the ratioof the water.-.vaporpressurel tothe t squareof lthe;nitricacid vapor pressure atvterriperatureT `over anitric acid-water solution rcontaining vthesamewp-roportions; of `l-INO3 and AH2O as` saidv aqueous; nitricacidcontaining substan-` whichiinitially contacts with gasrcontaining 'niFstronger nitric acid which comprises contacting a gas containingnitrogen peroxide and chlorine with an aqueous nitric acid solutioncontaining substantially 70 parts or more HNOa to 30 parts H2O, said gascontaining nitrogen peroxide, chlorine and nitrosyl chloride in amountssuch that is atleast equal to the antiloguo) of (0.02T--6.6) where:(NO2), (Cl-land (NOCI) are the partial pressures (in atmospheres) ofNO2, C12 and NOCl, respectively, in the gas with which the '70% orstronger nitric acidforrned by `reaction of the nitrogen peroxide withsaid. aqueous nitric acid is last contacted, T is the temperature indegrees absolute of the gas andnitric acid where the nitric acid is lastcontacted with the gas, and` (H20) (HNO3)2 isthe ratio of the watervapor pressure to the square ofthe nitric acid vapor pressure attemperature T over anitric acid-water lsolution containingthe sameproportions of HNO; and H2O as said. aqueous nitric Aacidcontainingmsubstantia1ly70 parts or more HNOa to 30 parts H2O whichinitially contacts with gas containing nitrogen peroxide and chlorineand nitrosyl chloride and a nitric acid containing at least parts HNO3to 30 parts H2O which is more concentrated than said aqueous nitric acidare formed by reaction of said nitrogen peroxide and chlorine with watercontained in said aqueous nitric acid, oxidizing said nitrosyl chlorideby means of oxygen, to form nitrogen peroxide and chlorine and reactingthe products 'of` said oxidation together With additional nitrogenperoxide with aqueous nitric acid to form concentrated nitric acid bythe aforedescribed steps.`l

`5. The process for the production of a concentrated nitric acidWhichcomprises passing a gas containing nitrogen peroxide and chlorinein thel proportions of 1 mol chlorine to 3 to 6 mols nitrogen peroxidein contact and in countercurrent iiow with an aqueous nitric acidcontaining about 68% to '74% HNOa, together with added Water whichdilutes said aqueous acid, continuing the treatment of the aqueousnitric acid with nitrogen peroxide and chlorine until the resultingconcentrated nitric acid contains about 1% chlorine (calculated as HC1)land HNOa and water 'in the same proportions as in a water solution ofnitric acidcontaining about to 90%`HNO3, said gas containing nitrogenperoxide and chlorine in amounts such that Y Where: (NO2), (C12)` and(NOCI) are the partial,

pressures (inatmospheres) of NO2, C12 and NOCI, respectively, in the gaswith which the acid of 80% to 90% HNOa strength formed by reaction ofthenitrogen peroxide -and chlorine with the yaqueous nitric acid islastcontacted, T is the temperature in degrees absolute o! thegas .andv`-nitric acid where the nitric acid is last contacted-` Withthev-gas, andf (HNOQJZ v.

is the ratio of the water vapor pressure to the square of the nitricacid vapor pressure at tem; perature T over a nitric acid-Water solutioncontaining: '70% HNO3, fractionally distilling thel concentrated nitricacid thus formedto obtain r an aqueous nitric acid residue containingabout 68% to 74% I-INO3 and a concentrated nitric acid v containingabout to 100% I-INOa, and treat-1v ing said aqueous nitric acid residuetogether with additional water with nitrogen peroxide and` r chlorineandrecovering from the resulting prod-.iv

uct aqueous nitric acid and concentrated nitric acid by the aforesaidsteps.

6. In a process for the production of concentrated nitric acid byreacting nitrogen peroxide and `an aqueous nitric acid containingsubstan' tially 70 parts or more HNOs to 30 parts H2O to form a nitricacid containing an increased proportion of HNOa to H2O that improvementwhich aqueous nitric acid in a reaction mixture con-H tainingconcentrations of nitrogen peroxide and tion of a nitric acid containingdissolved thereo irl mre than 0.5% total chlorine (calculated as HC1).7. In a process for the production of concentrated nitric acid byreacting nitrogen peroxidev and an' aqueous nitric acid containingsubstanl' tially '70 parts or more HNOa to 30 parts H2O to form` 'anitric acid containing an increased proportion ofV HNOa to H2O thatimprovement which comprises reacting said nitrogen peroxide and aqueousnitric acid in a reaction mixture containing concentrations of nitrogenperoxide and nitric acid for which the equilibrium partial pres-'Q sureof nitric oxide is below 0.01 atmosphere,k said reaction mixture.containing in the liquid phase thereof 1 mol of free chlorine to 5 to100v mols of nitrogen peroxide to reduce the partial pressure of nitricoxide of the reaction mixture o l to below said equilibrium partialpressure andk containing said chlorine, nitrogen peroxide and H2O andI-INOs in said aqueous nitric acid in proportions resulting in theformation of a'v nitric acid containing dissolved therein about 1% ormore total chlorine (calculated as HC1).

8. The process for the productionY of concentrated nitric acid whichcomprises contacting.`

nitrogen peroxide and chlorine with an aqueous nitric acid containingsubstantially '70 parts or more HNOa to 30 parts H2O in a reactionmixture which comprises a gas phase containing nitrogenq.

peroxide and chlorine in amounts such that Where: (NO2), (C12) and(NOCI) are the partial pressures (in atmospheres) -of NO2, C12 and NOCI,respectively,'in the gas phase with which the'70% or stronger 'nitricacid formedy by reactionof y '70 is at least equal to the antilognu) of(0.02T-6-6) I 'A comprises reacting saidV nitrogen peroxide and.` l

lns

the nitrogen peroxidewith said aqueous `nitric acid is last contacted, Tisthe temperature in degrees absolute of the reaction mixture in whichthe nitric acid is last contacted with the gas phase, and

(H20) (HNOS)2 is formed by reaction of said nitrogen peroxide andchlorine with Water contained in the aqueous nitric acid, fractionallydistilling the cony centrated nitric acidlthus formedto lobtain anaqueous'nitric acid residue and a more concentrated nitric acid andtreating said aqueous nitric acid residue with `nitrogen peroxide andchlorine and recovering from the resulting product aqueous nitric acidand concentrated nitric acid by the aforesaid steps.

9. The process for the production of or stronger nitric acid whichcomprises contacting a gas containing nitrogen peroxide and chlorine inthe proportions of 1 mol of ireechlorine for every 1 to 20 mols ofnitrogen peroxide With an aqueous nitric acid solution; containingsubstantially 70 parts or more HNO3 to 30 parts H2O, said gas containingnitrogen peroxide', chlorine and nitrosyl chloride in amounts such thatn (NOC1)(HN0)2 is at least equal to the antiloguo)` of (0.02T--6.6)Where: (NO2), (C12) and (NOCI) are the partial pressures (inatmospheres) of NO2, C12 and NOCl, respectively, in vthe gas with'whichthe 70% or stronger nitric acid formed by'reaction of thelnitrogenperoxide with said aqueous nitric acid is last contacted, T isthe temperature in degrees absolute of the gas and nitric acid Where thenitric acid is last contacted with vthe gas, and v trageny peroxide andchlorine and a nitric acid containing atleast 70 parts H1103 to 30 partsH2O Which is more concentrated than said aqueous nitricv acid is formedby reaction of said nitrogen peroxide and'chlorine with yWater containedin the aqueous nitric acid.

10. The process for the productionofv70% orf stronger nitric acid whichcomprises contacting a gas containing nitrogen peroxide and chlorine inthe proportions of 1 mol of free chlorine for every 3 to 6 lmols* ofnitrogen peroxide with an aqueous nitric acid solution'containingsubstantiaiiy 'zo parts'or more Hivos to 3o parts H20, said gasvcontaining nitrogen peroxide, chlorine and nitrosyl chloride in amountssuch that (N02)3(C12)1(H20) y (NOCIXHNOS)2 1s at least equal totheantiloguo) of (0.02T-6.6)

Where (NO2), (C12) and (NOCl) are the partial i pressures l (inatmospheres) of NO2, C12 and NOCl, respectively, in the gas with whichthe 70% nitrogen peroxide with said aqueous nitric acid is lastcontacted, T is the temperature in degrees or stronger nitric acidformed by reaction of the ,lo n

absolute of the gas and nitric acid Where the niv tric acidis lastcontacted with the gas, and

v is the ratiol of the water Vaporr pressure to the square of the nitricacid vapor pressure at temperature T` over a nitric acid-Water solutioncontaining the same proportions of HNOa and H2O as said aqueous nitricacid containing substantially 70 parts or more HNOS to 30-parts H2OWhich initially contacts with gas containing nitrogen peroxide andchlorine 'and a nitric acid containing at least 70 parts HNOa to 30parts H2O which is more concentrated than said aqueous nitric acid isformed by reaction of said nitrogen peroxide and chlorine withwatervcontained in the aqueous nitric acid.

1l. The process for the production of 70% or strongernitric acid whichcomprises contacting a gas containing nitrogen' peroxide and chlorine'in the proportions of 1 mol of free chlorine for every 3 to 6 mols ofnitrogen peroxide with an aqueous nitric acid solution containingsubstantiallyv 70 parts or more HNOa to 30 parts H2O, said gascontaining nitrogen peroxide, chlorine 'f and nitrosyl chloride Ainamounts such that is at least equal to the antiloguo) of (0.02T-6-6)where? (NO2), (C12) and (NOCI) are the partial pressures (inatmospheres) of NO2, C12 and NOCI, respectively, in the gas with whichthe '70% or stronger nitric acid formed byreaction of the nitrogenperoxide with said aqueous nitric acid is last contacted, T is thetemperature in degrees absolute of the gas and nitric acid where thevnitric acid is last contacted with the gas, 'and (H20) (HNOs)2 'is theratio of the vWater vapor pressure to the square of the nitric acidvapor pressure at temperature T over a nitric acid-water solutioncontaining the same proportions of HNOs and H2O as said aqueous nitricacid containing substantiallyy 70 parts or morev HNOa to 30 parts H2Owhich initially contacts With gas containing ni- CERTIFICATE OFCORRECTON.

Patentv No. 2,185,580. January 2, l9hO.

HERMAN A. BEEKHUIS, JR.

It is herehy certified that error appears in the printedy specificationof the above numbered patent requiring correction as follows: Page l,first column, line 514 for "dimittion" read limitation; page )4., firstcolumn, line 2T, for "nitrozen" read nitrogen; line 55 andsecond column,line second occurrence, for chloride read chlorine; line 56for "was"read with; and that the said Letters Pat-'ent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent O'fI'LCG.

Signed and sealed` this 6th day of February, A. D. 19LLO.

Henry Van Arsdale v(Seal) Acting Commissioner of .Patents.

